Recently, the laser display has been used more and more extensively (for example, it could be applied to the miniature projection device embedded in mobile phones, portable projects and laser TVs or the like). In the field of laser display, a discrete laser device with three base colors of Red, Green and Blue (RGB), which is low cost, small size, high efficiency and high power, is required urgently. Although the red and blue semiconductor laser diode can meet the cost/performance requirement of laser display, the green semiconductor laser diode cannot meet the requirement.
According to different types of projectors, the green laser needs a power of 100 mW to several watts. However, the green laser emitted from the current Diode Pumped Solid-state Laser (DPSSL) cannot meet the requirements of all laser display devices. For example, the DPSSL based on the optically contacted Neodymium doped Yttrium Orthovanadate (Nd:YVO4) and Potassium Titanyl Phosphate (KTP) can only generate green laser of less than 100 mW. Although the DPSSL made by separate Nd:YVO4 and KTP can generate green laser of more than 1 W, the requirement on strict size and cost cannot be met. The portable laser projector urgently needs a green laser which has the power of 300-1000 mW, high efficiency and small size.
By comparison with the KTP and Lithium Triborate (LBO) crystal in the prior art, the MgO doped Periodically Poled Lithium Niobate (MgO:PPLN) can generate green laser efficiently. Using 20 W 808 nm laser diode pump to generate green laser of 6 W has been recorded (Please refer to Y. Qi, et al., “High Power green laser with PPMgLN intracavity doubled,” CLEO/Pacific Rim '09, pp. 1-2, 2009), the MgO:PPLN crystal can also be used to achieve higher conversion efficiency (52%) (Refer to M. Zhou, et al., “52% optical-to-optical conversion efficiency in a compact 1.5 W 532 nm second harmonic generation laser with intracavity periodically-poled MgO:LiNbO3,” Laser Physics, vol. 20, no. 7, pp. 568-1571, 2010). However, these efficient discrete DPSS green lasers are achieved with a complicated packaging structure, for example, the components, such as laser diode, focusing lens, laser crystal (for example Nd:YVO4), nonlinear crystal (for example MgO:PPLN, KTP or LBO etc.) and output coupler and so on, have to be used in laser package. Therefore, it is impossible to massively manufacture so complex green laser devices. Furthermore, the discrete DPSS laser for generating green laser has a larger size, so it is not suitable for the field of laser display.
On the other hand, to generate green laser by means of optical contacted DPSSL is a mature technology, and has been reported in many literatures. For example, U.S. Pat. No. 5,365,539, Feb. 9, 1989. Moravian, et al., “Microchip laser”; U.S. Pat. No. 6,259,711, Jul. 10, 2001, F. Laurell, “Laser”; U.S. Pat. No. 7,742,510B2, Jun. 22, 2010, S. Essian, “Compact solid-state laser with nonlinear frequency conversion using periodically poled materials”; U.S. Pat. No. 7,570,676, Aug. 4, 2009, S. Essian, et al., “Compact efficient and robust ultraviolet solid-state laser sources based on nonlinear frequency conversion in periodically poled materials”; US patent application 2005/0,063,44100, D. C. Brown, “High-density methods for producing diode-pumped microlasers” etc. However, since the optical bonded interface has a low damage threshold, the output power of the green laser is also low. In order to overcome the problem of high power operation, Essian applied a microchip array structure (Please refer to U.S. Pat. No. 7,724,797B2, May 25, 2010, S. Essian, “Solid-state laser arrays using nonlinear frequency conversion using periodically poled materials”). Additionally, Yamamoto disclosed a planar waveguide DPSSL green laser structure (Please refer to U.S. Pat. No. 8,068,525, Nov. 29, 2011, S. Yamamoto, et. al., “Solid-state laser element”), wherein in order to scale up the power, the planar waveguide Nd:YVO4/PPMgLN array is used. However, the beam array re-shaped thereafter is very complicated.